All improvement in the various known instruments of this kind have always been aimed, above all, at achieving the maximum possible stability of the broken-off bone fragments fixed in the instrument.
Thus, the original single needle passed through the bone fragment gave way to twin needles. Then the needles were installed in angular relationship or cruciformly. The principle of needle fixation in an arch was discarded in favor of using twin arches or rings. Hempel pioneered the idea of fixing needles in a ring (1929). In the Soviet Union, A. S. Pertsovskii was the first to apply this principle (1938). Ring fixation of needles cruciformly passed through the bone was successfully performed in 1951 by G. A. Ilizarov (U.S.S.R. Inventor's Certificate No. 98,471 with priority, granted June 9, 1952). Elsewhere, Wittmoser in 1953 published his proposal to pass needles fixed in a ring in cruciform manner.
In this way, step by step, from the first days of recognition of the principles of compression and distraction, there has been evolved an independent, extremely promising method of compression-distraction osteosynthesis.
The most advanced and well-tried instruments of Soviet made embodying the above principle are those designed by G. A. Ilizarov, K. M. Sivash and O. N. Gudushauri. The underlying idea behind all practically used compression-distraction designs is a desire to achieve the maximum possible stability of the bone fragments. Of the known instruments, G. A. Ilizarov's one, using simple rings and a cruciform principle of needle introduction, comes closest to the ideal as far as bone fragment stability is concerned.
Most of the known compression-distraction instruments are built around three basic elements.
First of all, there are transaxially passed needles or rods introduced singly, in parallel or in cruciform relationship.
Secondly, there are arches or rings of various forms adapted to fix the ends of the needles or rods.
Thirdly, there are helical rods serving to interconnect the arches or rings of the instrument into a single whole and providing for a proportioned displacement and inclination of the individual arches or rings.
There exist a few designs, however, which use transaxially introduced rods but without recourse to arches or rings for interconnecting same.
At first sight, one may get an impression that the instruments built around the most advanced versions of the three elements described (namely, cruciformly introduced needles, rings and solid helical rods) are the final and optimal solution to all the problems associated with compression-distraction osteosynthesis. G. A. Ilizarov's and Wittmoser's instruments are examples of such designs. However so far the designers have concentrated only on the former two elements -- the method of transaxial introduction of needles and the means for fixing the free ends of the needles, such as arches and rings -- in their quest for improving compression-distraction instruments, almost entirely overlooking the importance of the helical rods interconnecting the arches and the rings.
Thus, said known instrument designed by G. A. Ilizarov has a serious disadvantage of requiring a complex procedure for matching dislocated bone fragments. Another drawback of this prior art instrument consists in that it is difficult to change the relative positions of the bone fragments in the course of permanent compression (distraction).
Besides, this prior art instrument does not allow additional, e.g. reinforcing, rings to be installed without adversely affecting the compressive (distractive) effect of the instrument.
Still another disadvantage of the known instrument consists in that permanent compression (distraction) of bone fragments cannot be maintained should the needle tension slacken, in cases of ossifluence, needle deformation, etc.
Furthermore, the known instrument does not permit controlling the direction of the instrument axis, bending or straightening it while permanently maintaining compression (distraction).